In recent years, along with an increase in communication traffic, an optical communication network using an optical fiber is required to have a higher capacity. In particular, Ethernet® serving as a main standard element of the communication network is becoming higher in capacity. Along with such an increase in capacity, the Ethernet standardization has been completed for 10 GbE and 40 GbE. The standardization process for 100 GbE aiming at an even higher capacity is almost complete.
As shown in FIG. 18, in an arrangement example of a 100 GBase-LR4/ER4 optical transmission system, an LD driver using a shunt circuit arrangement has been reported as an LD driver capable of performing high-speed operation at low power consumption in a transmission front end surrounded by a broken line.
In an arrangement example of a transmission front end using a shunt LD driver, as shown in FIG. 19, a portion surrounded by a broken line is a shunt LD driver portion. By adding the shunt LD driver portion parallel to an LD, a switch in the LD driver portion is turned on/off to carry information, as shown in FIGS. 20A, 20B, 20C, and 20D (FIG. 4 in Non-Patent Literature 1). Since the shunt LD driver has a high output resistance, the driver is integrated monolithically with the LD or mounted in the same package with the LD. Accordingly, impedance matching need not be performed, and high-speed operation can be performed at low power consumption.